Golf balls generally include a spherical outer surface with a plurality of dimples formed thereon. Historically dimple patterns have had an enormous variety of geometric shapes, textures and configurations. Primarily, pattern layouts provide a desired performance characteristic based on the particular ball construction, material attributes, and player characteristics influencing the ball's initial launch conditions. Therefore, pattern development is a secondary design step, which is used to fit a desired aerodynamic behavior to tailor ball flight characteristics and performance.
Aerodynamic forces generated by a ball in flight are a result of its translation velocity, spin, and the environmental conditions. The forces, which overcome the force of gravity, are lift and drag.
Lift force is perpendicular to the direction of flight and is a result of air velocity differences above and below the ball due to its rotation. This phenomenon is attributed to Magnus and described by Bernoulli's Equation, a simplification of the first law of thermodynamics. Bernoulli's equation relates pressure and velocity where pressure is inversely proportional to the square of velocity. The velocity differential—faster moving air on top and slower moving air on the bottom—results in lower air pressure above the ball and an upward directed force on the ball.
Drag is opposite in sense to the direction of flight and orthogonal to lift. The drag force on a ball is attributed to parasitic forces, which consist of form or pressure drag and viscous or skin friction drag. A sphere, being a bluff body, is inherently an inefficient aerodynamic shape. As a result, the accelerating flow field around the ball causes a large pressure differential with high-pressure in front and low-pressure behind the ball. The pressure differential causes the flow to separate resulting in the majority of drag force on the ball. In order to minimize pressure drag, dimples provide a means to energize the flow field triggering a transition from laminar to turbulent flow in the boundary layer near the surface of the ball. This transition reduces the low-pressure region behind the ball thus reducing pressure drag. The modest increase in skin friction, resulting from the dimples, is minimal thus maintaining a sufficiently thin boundary layer for viscous drag to occur.
By using dimples to decrease drag and increase lift, most manufactures have increased golf ball flight distances. In order to improve ball performance, it is thought that high dimple surface coverage with minimal land area and symmetric distribution is desirable. In practical terms, this usually translates into 300 to 500 circular dimples with a conventional sized dimple having a diameter that typically ranges from about 0.120 inches to about 0.180 inches.
Many patterns are known and used in the art for arranging dimples on the outer surface of a golf ball. For example, patterns based in general on three Platonic solids: icosahedron (20-sided polyhedron), dodecahedron (12-sided polyhedron), and octahedron (8-sided polyhedron) are commonly used. The surface is divided into these regions defined by the polyhedra, and then dimples are arranged within these regions.
Additionally, patterns based upon non-Euclidean geometrical patterns are also known. For example, in U.S. Pat. Nos. 6,338,684 and 6,699,143, the disclosures of which are incorporated herein by reference, disclose a method of packing dimples on a golf ball using the science of phyllotaxis. Furthermore, U.S. Pat. No. 5,842,937, the disclosure of which is incorporated herein by reference, discloses a golf ball with dimple packing patterns derived from fractal geometry. Fractals are discussed generally, providing specific examples, in Mandelbrot, Benoit B., The Fractal Geometry of Nature, W.H. Freeman and Company, New York (1983), the disclosure of which is hereby incorporated by reference.
However, the current techniques using fractal geometry to pack dimples does not provide a symmetric covering on the Euclidean spherical surface of a golf ball. Further, the existing methods does not allow for equatorial breaks and parting lines.